US Defence Secretary Ash Carter said on Wednesday that defence ministers from France and five other countries have agreed to intensify the campaign against the Islamic State group in Iraq and Syria.

Speaking at a news conference with France's Defence Minister Jean-Yves Le Drian, Carter said there was broad agreement on a coordinated plan to battle the IS group over the next year and take back key cities in Iraq and Syria from the militants.

"We agreed that we all must do more," Carter said shortly after a working lunch with Le Drian and defence ministers from France, Australia, Germany, Italy, the Netherlands and the United Kingdom.

Carter also announced that the 26 nations in the anti-IS group coalition, as well as Iraq, will meet in Brussels next month to continue the talks. Carter urged the coalition to seize the opportunity now to hasten the Islamic State group's defeat.

The US has mapped out a coordinated campaign against IS over the next year, and Carter laid out the plans to the ministers during the meeting, which was co-hosted by France.

"Because Daesh is retreating and we have managed to affect its resources in the ground, it is the moment to increase our collective forces with a coherent military strategy," Le Drian said, using another name for the Islamic State group, which is also known as ISIS and ISIL.

Carter has said he wouldn't hesitate to challenge core nations to do more in the fight in the coming year.

‘Raqqa and Mosul must be won back’

The defence ministers also discussed plans to retake two major IS group strongholds in Iraq and Syria. The coalition wants to help Iraqi and Kurdish peshmerga forces retake Mosul in northern Iraq and to assist the Syrian moderate forces in ousting Islamic State group militants from the Syrian city of Raqqa, the group's self-proclaimed capital.

"Raqqa and Mosul must be won back," Le Drian said, adding that it can only succeed if the coalition supports the local forces on the ground in Iraq and Syria.

US military leaders say the coalition is gaining ground on the IS group. And they are hoping that the six core nations can encourage others to contribute.

While European nations have been heavily involved, the US would like to see more direct military support – both equipment and training – from Arab and Asian countries. Arab nations joined the coalition's airstrike campaign early on, but their participation has waned over time, particularly as the fight between Saudi Arabia and Iran-backed rebels in Yemen has increased.

Before the meeting began, British Defence Minister Michael Fallon said Wednesday that the IS group is now under pressure and the goal of the gathering was to "identify how we can tighten the noose around the head of the snake”.

"We are now seeing Daesh being hit in its own heartland. We are seeing the attacks on its oil wells and we are beginning to see attacks [in Mosul],” Fallon told reporters. He said Britain carries out air strikes six days per week, plus reconnaissance flights to pinpoint targets.

The US has already asked allies to increase their contributions, including special operations forces, fighter jet and reconnaissance aircraft, weapons and munitions, training and other combat support. But the key needs are trainers and surveillance assets, such as drones.

Iraqi security forces, which waged a long battle to retake Ramadi, need increased training on niche capabilities, including how to counter improvised explosive devices.